1. Field of the Invention
The present invention relates to an information storage system including a magnetic head and a magnetic recording medium and, more particularly, relates to a portable magnetic hard disk drive having an improved shock resistance performance particularly during operation.
2. Description of the Background
The magnetic hard disk used in current magnetic hard disk drives typically includes a structure in which servo areas and data areas divided into a plurality of sector blocks are formed on concentrically formed tracks as shown in FIG. 6. In each of the servo areas, a specific bit pattern referred to as a servo pattern is recorded. Accurate information about the positioning of the magnetic head is performed by obtaining a head position signal from the servo pattern. The servo pattern typically includes an ISG (Initial Signal Gain) field, an SVAM (Servo Address Mark) field, a Gray code field, a burst field, a padding field, and other information as generally shown in FIG. 7.
When an external shock is applied to a magnetic hard disk drive during a recording operation of a magnetic head, the magnetic head may be displaced in the direction of track width. When this displacement occurs, the recording operation is preferably aborted so that adjacent tracks are not overwritten. In JP-A-97770/1998, there is disclosed a technology where a parity bit is provided at the boundary between adjacent tracks in a servo area in order to detect in which direction a head has moved (either an inward or outward radial direction of the disk) upon the occurrence of a positional displacement of the head. Further, for a compact magnetic hard disk drive, there may be a continuous monitoring for an external shock in which the compact magnetic hard disk drive further includes an acceleration sensor as described below.